Comprehensive 4D Parallel Transmission Spatial-Spectral Pulse Design for Slab-Selective Uniform Water-Selective...

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Radiofrequency (RF) Pulse Design
• Biomedical Engineering

Background:

• Achieving precise slab-selective excitation is crucial for MRI.
• Simultaneous water-selective excitation and fat suppression remain challenging.
• Existing methods struggle with out-of-slab fat excitation and uniformity.

Purpose of the Study:

• To introduce a novel parallel transmission (pTx) spatial-spectral (SPSP) pulse design.
• To achieve uniform water-selective excitation within a defined slab.
• To eliminate unwanted fat excitation outside the targeted slab using bipolar gradients.

Main Methods:

• Developed pTx SPSP pulses by formulating the design in 4D space (1D spectral, 3D spatial).
• Incorporated a SPINS-like 2D excitation k-space trajectory for flip-angle homogenization.
• Validated the design at 7 Tesla using simulations, phantoms, and human experiments with an 8-channel head coil.

Main Results:

• The new design demonstrated superior performance compared to traditional multi-spoke pTx SPSP pulses.
• Achieved slab-selective, uniform water-selective excitation with no out-of-slab fat excitation.
• Reduced excitation non-uniformity, measured by coefficient of variation, by up to approximately 23%.

Conclusions:

• The proposed pTx SPSP pulse design offers an effective solution for uniform water-selective excitation.
• This technique shows promise for mesoscale BOLD fMRI and fat-free body imaging at ultrahigh fields.
• Enables sharper slab profiles and improved image quality in advanced MRI applications.